Reassignment of the O2 spectrum just below dissociation threshold based on ab initio calculations

Abstract

Vibrational Herzberg bands of the O 2 molecule just below its first O( 3 P)ϩO( 3 P) dissociation limit are since long-known to be perturbed. Jenouvrier et al. ͓J. Mol. Spectrosc. 198, 136 ͑1999͔͒ assigned the cause of the perturbations to five vibrational levels supported by the shallow minimum in the 1 3 ⌸ u potential energy curve around 5.5a 0 . Using ab initio potential energy curves and spin-orbit couplings from previous work ͓J. Chem. Phys. 116, 1954 ͑2002͔͒ we present a full quantum calculation of all ungerade rotation-vibration-electronic states of oxygen just below the dissociation threshold, through a total angular momentum quantum number of Jϭ19. This calculation shows that the original assignment, based on a Hund's case ͑a͒ model of a regular 1 3 ⌸ u multiplet was not correct. Based on our calculation we present a new assignment of the perturbing states: 1 3 ⌸ u,⍀ϭ2 (vϭ0͒, 1 3 ⌸ u,1 ͑0͒, 1 3 ⌸ u,2 ͑1͒, 1 3 ⌸ u,1 ͑1͒, and 1 3 ⌸ u,0 Ϫ͑0͒ in order of ascending term values. We show the new assignment to be consistent with experimental data and we also propose new spectroscopic parameters for the perturbing states.

Theoretical study on the photoabsorption in the Herzberg I band system of the O2 molecule

“…For instance, the difference between the HundÕs case (a) and HundÕs case (c) potential curves is rather large in spite of the small SO interaction for the v 0 = 12 level. This point was also discussed by Vroonhoven et al [36]. Other theoretical values [20] were in better agreement with experiment than ours except for the v 0 = 12 level.…”

Accurate ab initio potential energy curve of O2. II. Core-valence correlations, relativistic contributions, and vibration-rotation spectrum

“…Among these 18 states, there are six bound states with the respective 3 ⌬ u , and 3 ⌺ u + , shown at the lower left of Fig. 10,11 Most important are the three low lying bonding states, 3 ⌺ g − , 1 ⌬ g , and 1 ⌺ g + . 10,11 Most important are the three low lying bonding states, 3 ⌺ g − , 1 ⌬ g , and 1 ⌺ g + .…”

“…It is reckoned 1-4 that the appearance of O 2 in the environment, around 2.2ϫ 10 9 years ago, had a revolutionizing effect on biochemical networks and the evolution of complex life. [8][9][10][11] The O 2 molecule manifestly plays a manifold role in the maintenance of life on earth. Since the majority of the reactions with organic molecules are with singlets, they are spin forbidden implying that they are slow at ambient conditions, a circumstance that represents a problem for living organisms wanting to employ O 2 in their metabolism.…”

Photodissociation of O2 via the Herzberg continuum: Measurements of O-atom alignment and orientation

“…The case ͑c͒ potentials were obtained by diagonalization of the matrix elements of the Hamiltonian Ĥ ϭĤ Coul ϩĤ SO in the basis of the electronic states for ⍀ϭ0, 1, 2, and 3, respectively, as a function of the internuclear separation, R. The eigenvalues of the Coulombic Hamiltonian Ĥ Coul correspond to the electronic adiabatic Born-Oppenheimer ͑ABO͒ states, and the matrix elements of Ĥ SO are the spin-orbit couplings between ABO states. 24 Equations ͑11͒-͑14͒ show how Im͓a 1 (1) ( ʈ ,Ќ)͔ is related to the potential energy curves E n (R) through the phase accumulated during dissociation at a given available energy E. When the available energy is much larger than the potential energy difference between parallel and perpendicular curves, the phase difference ⌬ does not vary much, and the Im͓a 1 (1) ( ʈ ,Ќ)͔ will change very slowly as a function of the photolysis energy. Nearer to threshold, however, ⌬ varies more rapidly with E, and measurement of the energy dependence of Im͓a 1 (1) ( ʈ ,Ќ)͔ can be a very sensitive test of the shapes of the potential energy curves.…”